Prior art catheter and bolus inventions are disclosed in U.S. Pat. No. 4,594,074, U.S. Pat. No. 5,451,216, U.S. Pat. No. 5,599,322 and U.S. Pat. No. 5,810,787. U.S. Pat. No. 4,594,074, for example, addresses catheter bolus construction as it relates to both aspiration and outflow. The side walls of the bolus at the bolus port are recessed to a height of no more than one half of the internal diameter (ID) of the bolus passage. Lowering the walls below this minimum level would result in bending of the tube. Practically speaking, in the preferred embodiment of this particular catheter bolus, the height of the side the walls bracketing the bolus port must actually be at the full height of the bolus passage.
The three other patents referred to describe a catheter which allows the side walls of the bolus to have a height which is less than one half of the outside diameter of the body. This is accomplished by using side walls that have a continuously curving slope and by providing a body segment that includes a structural arch component protruding radially outward therefrom. This design provides a recessed, protected port that is larger than the port in the catheter bolus of U.S. Pat. No. 4,594,074 while still preventing the bolus from kinking and restricting the port.
The tip boluses disclosed in all of these patents are what are referred to as “smooth” boluses. They are glued over the tube. Usually, the socket of the bolus has side walls that are 0.015 inches thick. The tip bolus is slightly larger than the tube, but only as large as is necessary to form the gluing socket. For an example, a 12FR feeding tube has an outside diameter of 0.158 inches. The OD of the 12FR smooth tip bolus is 0.188, or 0.030 larger than the tube so as to incorporate the socket walls. Thus, the bolus thickness OD is increased to slightly more than that of a 14FR tube (0.184 inches). This increase in thickness from tube to bolus is not important in a nasogastric feeding tube because the tube can easily be passed through the nose, and the size of the tube remaining in the nares is the major factor in patient comfort.
Some nasogastric feeding tube designs have tip boluses that are purposefully made much larger than the tubing for operational purposes. These designs are referred to as “large” boluses or “fat” boluses and are designed provide a shape which is ideal for gripping by peristalsis. Fat boluses are commonly attached to 8FR, 10FR and 12FR tubes and have outside diameters of 0.230 inches, which is considerably larger than even the OD of a 12FR tube, for example.
Difficulty of insertion and clogging of the catheter have heretofore restricted the use of gastric/jejunal feeding tubes or catheters. However, it is generally recognized that jejunal placement is preferred over gastric or duodenally placed catheters. Duodenal placement solves some of the problems of pulmonary aspiration, but the incidence of such aspiration is still 20%. Tubes pull out of the duodenum easily and feeding material leaks back into the stomach. In contrast, the jejunum has strong peristalsis resisting pull-out, and the curves leading to it from the stomach also help resist inadvertent removal.